In recent years, in the light of internationalization of physical distribution or mass transit, a marine transportation is frequently performed, and travel of a semi-trailer (a traction vehicle) transporting a marine container is frequently performed. Further, in the container transportation, it is possible to suppress discharge of CO2 which causes global warming by utilizing a public mass transit network such as railroads in addition to marine vessels, that is, by restricting the transportation by the trailer in land transportation.
As a result, the container transportation by the semi-trailer is assumed to be movement of the container from unloading from the marine vessel to a container yard, transportation from the container yard to a railway container station, and transportation of the container from the container yard to a consignor.
Here, a description will be given of the semi-trailer with reference to FIG. 8. A semi-trailer 1X is constructed by a trailer 3 which has a container 4 on board, and a tractor head 2X which tows the trailer 3, and the tractor head 2X comes to a vehicle equipped with an engine 10X which includes an engine main body 11X having a large displacement, and a power train 20X which includes a large-scaled multi-stage transmission 21X, for towing the trailer 3 which has the container 4 on board. In order to improve a fuel consumption of the semi-trailer 1X, downsizing and speeding down are promoted in relation to the engine 10X and the power train 20X in recent years.
The transportation of the marine container 4 by the semi-trailer 1X can hold down an energy consumption for the transportation by performing the transportation linked with the other mass transportation modes. However, in relation to the structure of the trailer 3, a mode of packing which can be boarded on is limited to the standardized marine container 4 or the structure conforming to the standardized marine container 4. Therefore, after transporting the cargo to the transport destination, the tractor head returns to the container yards or harbor facilities while towing the container 4 or the trailer 3 having the container 4 on board if the same container 4 of the trailer 3 having the container 4 on board exists at the transport destination. However, in other cases, the tractor head 2X returns while towing the trailer 3 which does not have the container 4 on board, or only the tractor head 2X travels back without the trailer 3.
Since the tractor head 2X towing the trailer 3 originally aims at towing the trailer 3 which has the container 4 on board, the engine 10X having a large displacement and a high output, and the large-scaled multi-stage transmission 21X are mounted on the tractor head 2X. However, as mentioned above, the necessary engine output is apparently different in the travel only by the tractor head 2X, or the travel in the state of towing the trailer 3 on which the container 4 is not mounted, from the state in which the container 4 is mounted, and the engine 10X is used in a low output state. Therefore, the gear stage which is provided in the engine 10X of a large scale and the high output and the large-scaled multi-stage transmission 21X and which is required at the starting time in the state having the container 4 on board is not necessary.
More specifically, in the travel having the container 4 on board, the engine 10X having the large displacement, the high output and the high torque, and the multi-stage transmission 21X are required, while in the travel only by the tractor head 2X or the travel in the state having no container 4 on board, it is possible to travel with a small displacement engine and a small-scaled multi-stage transmission (here, the small-scaled multi-stage transmission indicates a transmission having fewer gears by doing away with the gear stage which is used at the starting time or at the transient time (for example, at the accelerating time from the low speed) in the state in which the trailer has the container on board.
In connection with the above, there is an apparatus which is structured such as to select a control pattern of a boost characteristic according to a loaded condition and an empty condition which are detected by a road sensing switch, and controls an instructed injection amount according to the boost characteristic pattern which reduces the injection amount at about 20% in the empty condition (refer, for example, to patent document 1).
Further, there is also an apparatus which realizes the high torque in a whole of an engine working range and achieves improvement of the fuel consumption and the output, by using an engine which is based on combination of a two-stage turbo system and a VGS (a variable blade turbo mechanism) and has a small displacement and a highly supercharging, the two-stage turbo system being obtained by combining a high-pressure stage turbocharger and a low-pressure stage turbocharger with the engine having the small displacement.
However, since an exhaust gas energy is utilized in the supercharging mentioned above, supercharge response delay, that is, a turbo lag is generated in the supercharging at the starting time from the idling having less exhaust gas energy, and the supercharging under the rapid transit to the transient state from the steady operation state. As a result, there is a problem that torque shortage is generated at the starting time and the transient time, or a problem of smoke. These problems are particularly significant in the semi-trailer in which a loading amount significantly varies.
Here, as a device configured to improve a starting torque and improve a transient supercharging characteristic, it is thought to utilize a supercharger (a mechanical supercharging device; hereinafter refer to as S/C) which picks up rotary motion from an engine crank shaft so as to supercharge. However, in the supercharging by the S/C, there is generated a case that the fuel consumption is deteriorated due to drive loss of the S/C particularly in a high speed side of the engine running speed.